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Code Review Guidelines
This document provides TF-A specific details about the project's code review
process. It should be read in conjunction with the `Project Maintenance
Process`_, which it supplements.
Why do we do code reviews?
The main goal of code reviews is to improve the code quality. By reviewing each
other's code, we can help catch issues that were missed by the author
before they are integrated in the source tree. Different people bring different
perspectives, depending on their past work, experiences and their current use
cases of TF-A in their products.
Code reviews also play a key role in sharing knowledge within the
community. People with more expertise in one area of the code base can
help those that are less familiar with it.
Code reviews are meant to benefit everyone through team work. It is not about
unfairly criticizing or belittling the work of any contributor.
Good practices
To ensure the code review gives the greatest possible benefit, participants in
the project should:
- Be considerate of other people and their needs. Participants may be working
to different timescales, and have different priorities. Keep this in
mind - be gracious while waiting for action from others, and timely in your
actions when others are waiting for you.
- Review other people's patches where possible. The more active reviewers there
are, the more quickly new patches can be reviewed and merged. Contributing to
code review helps everyone in the long run, as it creates a culture of
participation which serves everyone's interests.
Guidelines for patch contributors
In addition to the rules outlined in the :ref:`Contributor's Guide`, as a patch
contributor you are expected to:
- Answer all comments from people who took the time to review your
- Be patient and resilient. It is quite common for patches to go through
several rounds of reviews and rework before they get approved, especially
for larger features.
In the event that a code review takes longer than you would hope for, you
may try the following actions to speed it up:
- Ping the reviewers on Gerrit or on the mailing list. If it is urgent,
explain why. Please remain courteous and do not abuse this.
- If one code owner has become unresponsive, ask the other code owners for
help progressing the patch.
- If there is only one code owner and they have become unresponsive, ask one
of the project maintainers for help.
- Do the right thing for the project, not the fastest thing to get code merged.
For example, if some existing piece of code - say a driver - does not quite
meet your exact needs, go the extra mile and extend the code with the missing
functionality you require - as opposed to copying the code into some other
directory to have the freedom to change it in any way. This way, your changes
benefit everyone and will be maintained over time.
Guidelines for all reviewers
There are no good or bad review comments. If you have any doubt about a patch or
need some clarifications, it's better to ask rather than letting a potential
issue slip. Examples of review comments could be:
- Questions ("Why do you need to do this?", "What if X happens?")
- Bugs ("I think you need a logical \|\| rather than a bitwise \|.")
- Design issues ("This won't scale well when we introduce feature X.")
- Improvements ("Would it be better if we did Y instead?")
Guidelines for code owners
Code owners are listed on the :ref:`Project Maintenance<code owners>` page,
along with the module(s) they look after.
When reviewing a patch, code owners are expected to check the following:
- The patch looks good from a technical point of view. For example:
- The structure of the code is clear.
- It complies with the relevant standards or technical documentation (where
- It leverages existing interfaces rather than introducing new ones
- It fits well in the design of the module.
- It adheres to the security model of the project. In particular, it does not
increase the attack surface (e.g. new SMCs) without justification.
- The patch adheres to the TF-A :ref:`Coding Style`. The CI system should help
catch coding style violations.
- (Only applicable to generic code) The code is MISRA-compliant (see
:ref:`misra-compliance`). The CI system should help catch violations.
- Documentation is provided/updated (where applicable).
- The patch has had an appropriate level of testing. Testing details are
expected to be provided by the patch author. If they are not, do not hesitate
to request this information.
- All CI automated tests pass.
If a code owner is happy with a patch, they should give their approval
through the ``Code-Owner-Review+1`` label in Gerrit. If instead, they have
concerns, questions, or any other type of blocking comment, they should set
Code owners are expected to behave professionally and responsibly. Here are some
guidelines for them:
- Once you are engaged in a review, make sure you stay involved until the patch
is merged. Rejecting a patch and going away is not very helpful. You are
expected to monitor the patch author's answers to your review comments,
answer back if needed and review new revisions of their patch.
- Provide constructive feedback. Just saying, "This is wrong, you should do X
instead." is usually not very helpful. The patch author is unlikely to
understand why you are requesting this change and might feel personally
- Be mindful when reviewing a patch. As a code owner, you are viewed as
the expert for the relevant module. By approving a patch, you are partially
responsible for its quality and the effects it has for all TF-A users. Make
sure you fully understand what the implications of a patch might be.
Guidelines for maintainers
Maintainers are listed on the :ref:`Project Maintenance<maintainers>` page.
When reviewing a patch, maintainers are expected to check the following:
- The general structure of the patch looks good. This covers things like:
- Code organization.
- Files and directories, names and locations.
For example, platform code should be added under the ``plat/`` directory.
- Naming conventions.
For example, platform identifiers should be properly namespaced to avoid
name clashes with generic code.
- API design.
- Interaction of the patch with other modules in the code base.
- The patch aims at complying with any standard or technical documentation
that applies.
- New files must have the correct license and copyright headers. See :ref:`this
paragraph<copyright-license-guidance>` for more information. The CI system
should help catch files with incorrect or no copyright/license headers.
- There is no third party code or binary blobs with potential IP concerns.
Maintainers should look for copyright or license notices in code, and use
their best judgement. If they are unsure about a patch, they should ask
other maintainers for help.
- Generally speaking, new driver code should be placed in the generic
layer. There are cases where a driver has to stay into the platform layer but
this should be the exception, rather than the rule.
- Existing common drivers (in particular for Arm IPs like the GIC driver) should
not be copied into the platform layer to cater for platform quirks. This
type of code duplication hurts the maintainability of the project. The
duplicate driver is less likely to benefit from bug fixes and future
enhancements. In most cases, it is possible to rework a generic driver to
make it more flexible and fit slightly different use cases. That way, these
enhancements benefit everyone.
- When a platform specific driver really is required, the burden lies with the
patch author to prove the need for it. A detailed justification should be
posted via the commit message or on the mailing list.
- Before merging a patch, verify that all review comments have been addressed.
If this is not the case, encourage the patch author and the relevant
reviewers to resolve these together.
If a maintainer is happy with a patch, they should give their approval
through the ``Maintainer-Review+1`` label in Gerrit. If instead, they have
concerns, questions, or any other type of blocking comment, they should set
*Copyright (c) 2020, Arm Limited. All rights reserved.*
.. _Project Maintenance Process: